Vanessa Hudgens and boyfriend under police investigation for carving love message into a rock

Vanessa Hudgens won raves for nailing the role of Rizzo late last month in the TV musical Grease: Live, but Arizona police are not as impressed by the actress' "art".

The 27-year-old High School Musical star and her boyfriend, Arrow star Austin Butler, 24, are under investigation by Arizona authorities for defacing a rock formation in the US state's Coconino National Forest.

The legal drama began when Vanessa posted a since-deleted Instagram pic of "Austin + Vanessa" etched into a rock in the park. Under US law, it's illegal to damage or deface natural surfaces in the Red Rock Ranger District, which is where Vanessa and Austin spent Valentine's Day.

The picture, which earned almost 2,000 comments and 320,000 likes before being removed, was captioned: "Happy Valentine's Day boo boo bears".

Apparently, Arizona authorities were not feeling the love, as the Instagram post triggered the investigation.

The past few weeks have been the best and worst of times for Vanessa. Her father Gregory Hudgens died of cancer the night before her acclaimed Grease performance, and now her love day has been marred by possible legal entanglements…and a dose of Instagram hate.

Vanessa and Austin face a maximum fine of US$5000 and and/or six months of jail time.

Here's Vanessa and her fellow High School Musical alumni in January reliving happier happy days.

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